Millions of 02 customers have described their day from hell as the network crashed leaving some unable to work, and others fearing for the safety of relatives.
The IT fault at Britain’s second biggest mobile network left furious users cut off from online data services and apps – and many could not even make calls.
The telecoms giant has 25million customers. It also serves another seven million who are signed up to Tesco Mobile, Sky, GiffGaff and Lycamobile.
Jennie O’Grady is one such customer for whom yesterday's outage brought about immense stress and difficulty.
Jennie O’Grady (left), 39, from Glossop, Derbyshire was left unable to monitor her type-1 diabetic daughter Esme’s (right) blood glucose levels
Meanwhile, Luke Stagg (left), a heating engineer and plumber, said he has been unable to reach several customers due to the outage. And Amy-Jayne Toulson (right), a cleaner from Cirencester, Gloucestershire, suffers from epilepsy and has a watch that monitors for seizures and connects to her mobile phone – sending a message to her caregivers if she has a seizure
She relies on O2 data to monitor her type-1 diabetic daughter Esme’s blood glucose levels.
Esme’s phone links to a continuous glucose monitor that sends information to her mother’s phone to tell her if Esme’s blood sugar levels are dangerously high or low.
But yesterday, after Esme, 12, caught the bus to school and left her house’s wifi signal, Mrs O’Grady, from Glossop, Derbyshire, was unable to track the potentially life-saving data.
The mother-of-three, 39, said: ‘We rely massively on her having internet access. She can be sleeping in her bedroom and it is sending me her blood sugar levels.
‘I would get an alarm to say she is having a hypoglycaemic attack if her blood sugar levels dropped below four, which would mean she need treatment immediately and could go into a coma.
‘Without it I have been completely clueless and I have not been able to check on her.’
Meanwhile, Luke Stagg, a heating engineer and plumber, said he has been unable to reach several customers due to the outage.
The 36-year-old, from Tunbridge Wells, Kent, uses his phone’s data to find addresses on his map and says he runs his business through his mobile. He said: ‘I will take it on the chin, but no-one is going to pay for my losses today.’
Last night he said he had difficulty running his business because he was unable to contact customers while on the road or use sat nav.
‘That’s a whole day wasted,’ he said. ‘I’ll be seeking to recoup my losses, especially as a business customer.’
The outage was blamed on a failure in systems operated by O2’s equipment supplier, Swedish firm Ericsson – and even affected mobile phone services as far as Japan
O2 has been keeping customers updated on its website on the latest with the network outage, this was the picture early yesterday morning
And Amy-Jayne Toulson, a cleaner from Cirencester, Gloucestershire, suffers from epilepsy and has a watch that monitors for seizures and connects to her mobile phone – sending a message to her caregivers if she has a seizure.
The 30-year-old said: ‘For people who use their phone like I use it, your mobile phone is your lifeline.’
The system outage, which began just before 5am, was not expected to be fixed until around 9am today - although 02 informed customers on its social media channels last night that 3G service was returning.
A spokesman for the firm told MailOnline last night: 'Our 3G data service was restored this evening.
When did the network problem start?
The first reports of a loss of access to 4G data services on the mobile network appeared on social media at 4.50am.
Who was affected?
Some 25million customers signed to the O2 network, plus another 7million with Tesco Mobile, Sky Mobile, GiffGaff and Lycamobile, which offer services over the same system.
What services were lost?
Access to the internet, emails and apps such as Google maps over the mobile network were lost. Some customers also reported smartphone payments were interrupted. Electronic bus timetable updates on London bus shelters failed.
What about voice calls?
Voice calls continued operating initially. However as more phone owners resorted to making calls rather than sending emails, customers found the system straining under pressure.
What was the cause?
O2 blames software systems operated by the Swedish tech giant Ericsson as part of a global failure that also hit Japan.
Are customers owed compensation?
When customers experienced a seven-hour blackout in 2015, O2 said it would not be offering compensation because of the ‘length and effect of the incident’. It is not clear whether it will offer payouts in this case.
'Our technical teams will continue working hard with Ericsson engineers to restore 4G which will bring us back to full network service. We’re sorry for the loss of service our customers have experienced today.'
And later that same evening, the firm issued a statement to say it anticipated 4G being restored by 3am.
A spokesman said: 'Our technical teams have started to return our 4G service to our network.
'We anticipate this will be restored by 3am this morning meaning all our services will be fully restored.'
It is thought to be the largest and longest mobile internet blackout in the UK.
Now customers are asking what the company is going to do and the firm is expected to face a huge payout if forced to provide compensation.
Should each customer be issued with £5 credit, it would mean the firm has to pay out around £160 million.
Along with frustration to millions of individuals, the glitch hit satnav services in a blow to taxi firms, couriers and food delivery services.
Commuters relying on electronic bus timetables and traffic apps were also affected.
And customers were also blocked from using mobile payment services including Apple Pay and Google Pay – used by millions at shop tills or on transport networks.
Overburdened call lines later buckled as phone users switched to voice calls rather than sending text, Whatsapp or email messages.
Smart meters are also said to have been affected by the outage, as the devices rely on O2 data services - and installations of the devices were reportedly cancelled as a result.